Seems like your water could be a bit low at half a gallon. You may be cramping from dehydration if your workouts are vigorous enough. Slow increase is to .75 gallon ... 1 gallon, more of need be. BTW.. if you are not getting enough water, is one of the easiest way to kiss your muscle gains goodbye
As for sodium I always recommend people to use condiments with sodium, eg soy sauce, mustard, etc. Then you can add some sea salt to meals if you are still lacking.
Also some BCAA intra workout drinks have sodium... scivation xtend comes to mind.
Good luck and keep us posted!